I always go for a mattebox so that you can control your light a bit more (if you're using flags and doors). Any kind would work fine as long as it has at least two filter holders. If it has two (or more) filter holders one of them will be rotating for your grads and such.
As for filters, go to a rental house and ask if they have any that they're about to throw away, if they do they'll give them to you for free.
Hope that helps .
Good tip with the rental houses... hope you live nowhere near me so there are some left by the time I make my rounds..
Since I don't have camera here yet, what are typical connector/fitting issues?
(i.e. what other then lens diameter do I need to take into account to make sure the box is going to fit? The manual that I found says the lens thread diameter is 67mm)
Would you recommend anything in particular? This is really not my area of expertise...